Claire Squires collapsed within mile of finish line of 2012 London Marathon (Justgiving)

On 22 April, more than 37,000 people crossed the line and took on the challenge of the 2012 Virgin London Marathon. Some took less than three hours, some more than seven, but tragically one woman never finished.

Claire Squires, a 30-year-old from Leicestershire, collapsed at Birdcage Walk, within a mile of the finish line. Medical staff immediately realised that she was seriously unwell and, despite efforts to save her, she was pronounced dead. Her boyfriend, Simon Van Herrewege, was waiting for her at the finish line of the race.

Squires had gained a place in the marathon by entering her name into the ballot for places. She later decided that she would take the opportunity to raise money for the Samaritans charity. Before the race she had raised £650.

Five days after her death and the total has reached more than £795,000, £966,000 including Gift Aid.

How Claire Squires' fundraising page looked on 27 April (Justgiving)

On Squires's fundraising page, her message reads: "If everyone I know could donate £5, that would be a great help and change lives."

Squires will never know the impact of those words, as it was not just everyone she knew, but everyone they knew, and so on, that took the time to sign up and make a donation. So far, more than 69,000 donations have been made, the majority of which have left a message of support for Squires' family or a short tribute.

This is not the first time that someone has died running the London Marathon. Since the event began in 1981, 11 people have died. So what was it about the death of Squires that led to such a public response?

Obviously, the concept of a young, physically fit competitor dying in the course of any event is a huge shock, but ever-developing trends of internet communication gave the public a new way to react.

In recent years the term "viral" applies to something that spreads like wildfire across the internet, as instant communication gives an article, picture or video clip the ability to touch millions of people within hours.

The reaction to Squires' death shows the best side of the internet viral sensation. Squires' Justigiving page gave people the ability to make a tribute and donation, from anywhere in the world, within a few seconds, in a simple, selfless act, underlining Squires' own description of Samaritans as a charity that "continuously supports others".

Within a matter of hours, the avalanche of support for Squires' family saw celebrities give their backing to the fund and The Sun transformed it into a campaign to hit £1m, a goal that seems certain to be reached.

It is worth focusing on the positive impact of something going "viral" on the internet. When it is mentioned in the press, it often has to do with an unpleasant video, cyber bullying or disposable novelty humour. In this case, thousands of pounds have been donated to a charity, while Squires' family has been overwhelmed by the positive legacy that Claire will leave.

Constantly held up as the cause for diminishing attention spans and degrading human communication, the internet gave even the laziest web surfer the ability to be part of a worthy cause.

It is still not known what caused Squires to collapse and die during the race, but it has led to renewed warnings that marathons are extreme challenges that can be dangerous for people with underlying health problems, especially heart conditions.

Professor Sanjay Sharma, Virgin London Marathon's medical director, told the BBC that fatalities are very rare in marathons, with Squires being the first woman to die at the event.

He said: "We are still waiting for the post mortem on the young woman, but her death is likely to be due to a heart problem I should think.

"I was there at the arrest and was deepy shaken. To see a 30-year-old who is amazingly athletic die is so counterintuitive. These deaths are rare."